1. Field of the Invention
The present invention relates to a system for printing color image data using different inks. More particularly, the present invention concerns a system for printing color image data using black inks having different penetration qualities.
2. Description of the Related Art
Recently, systems have been developed for printing image data on a recording medium using both low-penetration and high-penetration black ink. Most commonly, low-penetration black inks used in such a system are pigment-based inks, while high-penetration black inks are dye-based. Low-penetration black inks offer greater optical density than high-penetration black inks, and are therefore desired for text and/or large black regions. In contrast, high-penetration black inks offer a similar optical density as that offered by colored inks, which are also high-penetration inks, and therefore high-penetration black inks are desired for use in colored regions of an image. Commonly-assigned U.S. application Ser. No. 08/972,308, filed Nov. 17, 1997 and entitled xe2x80x9cPrinting With Multiple Different Black Inksxe2x80x9d, describes a system in which low-penetration black inks are used to print black regions of an image and high-penetration black inks are used to print black pixels within colored regions of an image.
Despite the apparent advantages of the above-described usage of low-penetration and high-penetration black inks, images produced in this manner often appear discontinuous or nonuniform, due to the difference in optical densities of high-penetration and low-penetration black inks used to print the image. Accordingly, what is needed is a system to output black color in an image which provides uniform color images, crisp text in black regions, and an overall appearance of image uniformity.
The present invention addresses the foregoing problems by producing a binarized value corresponding to low-penetration black ink for use in printing a subject pixel and a binarized value corresponding to high-penetration black ink for use in printing the subject pixel. By virtue of the foregoing, smooth color regions, crisp text and black regions, and overall image uniformity can be obtained.
In a further aspect, low-density regions of an image are printed using a first droplet size of black ink and high-density regions of the image are printed using a second droplet size of black ink, the second droplet size being larger than the first droplet size. As a result, crisper text and large black regions can be obtained.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.